Since the discovery of penicillin in the 1920s and streptomycin in the 1940s, many new compounds have been discovered or specifically designed for use as antibiotic agents. It was once thought that infectious diseases could be completely controlled or eradicated with the use of such therapeutic agents. However, such views have been challenged because strains of cells or microorganisms resistant to currently effective therapeutic agents continue to evolve. Almost every antibiotic agent developed for clinical use has ultimately encountered problems with the emergence of resistant bacteria. For example, resistant strains of Gram-positive bacteria such as methicillin-resistant staphylococci, penicillin-resistant streptococci, and vancomycin-resistant enterococci have developed. Resistant bacteria can cause serious and even fatal results for infected patients. See, e.g., Lowry, F. D. “Antimicrobial Resistance: The Example of Staphylococcus aureus,” J. Clin. Invest., vol. 111, no. 9, pp. 1265-1273 (2003); and Gold, H. S, and Moellering, R. C., Jr., “Antimicrobial-Drug Resistance,” N. Engl. J. Med., vol. 335, pp. 1445-53 (1996).
The discovery and development of new antibacterial agents have been for decades a major focus in many pharmaceutical companies. Nonetheless, in more recent years there has been an exodus of pharmaceutical companies from this area of research and drug development. As a consequence of this exodus, there have been very few new antibiotics entering the market. This lack of new antibiotics is particularly disturbing, especially at a time when bacterial resistance to current therapies is increasing both in the hospital and community settings.
In the search for new antibiotic agents, researchers have tried combining or linking various portions of antibiotic molecules to create multifunctional or hybrid compounds Other researchers have tried making derivatives of known classes of antibiotics, e.g., telithromycin, which is sold under the trade name Ketek®, is a derivative of erythromycin. However, these approaches have met with limited success.
An approach to developing new antimicrobial compounds is to design modulators, for example, inhibitors, of bacterial ribosome function. By modulating or inhibiting bacterial ribosome function such antimicrobial compounds could interfere with essential processes such as RNA translation and protein synthesis, thereby providing an antimicrobial effect. In fact, some antibiotic compounds such as erythromycin, clindamycin, and linezolid are known to bind to the ribosome.
The present invention utilizes a structure based drug design approach for discovering and developing new antimicrobial agents. This approach starts with the high resolution X-ray crystal of the ribosome to design new classes of antimicrobial compounds having specific chemical structures, ribosome binding characteristics, and antimicrobial activity. This structure based drug discovery approach is described in the following publication: Franceschi, F. and Duffy, E. M., “Structure-based drug design meets the ribosome”, Biochemical Pharmacology, vol. 71, pp. 1016-1025 (2006).
Based on this structure based drug design approach, the present invention describes new chemical classes of antimicrobial compounds useful for treating bacterial infections in humans and animals. Without being limited by theories, these compounds are believed to inhibit bacterial ribosome function by binding to the ribosome. By taking advantage of these ribosome binding sites, the antimicrobial compounds of the present invention can provide better activity, especially against resistant strains of bacteria, than current antibiotic compounds.
The present invention therefore fills an important ongoing need for providing new antimicrobial agents, particularly for antimicrobial agents, having activity against resistant pathogenic bacterial organisms.